Electrolyte and lithium-ion battery containing the same

ABSTRACT

The present application relates to the technical field of lithium-ion batteries and, specifically, relates to an electrolyte and a lithium-ion battery containing the electrolyte. The electrolyte of the present application includes a lithium salt, an organic solvent and additives, the additives include a fluorinated ether compound and an ester dimer compound, the ester dimer compound includes carbonate dimers, carboxylate dimers and sultone dimers. The lithium battery adopting the electrolyte of the present application can realize the object of high voltage, of which the highest normal working voltage can be improved to 4.4˜5.0V, and the lithium battery has good cycle performance, such as higher capacity retention rate at charge or discharge and improved service life.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Chinese Patent ApplicationNo. 201610352232.2, filed on May 25, 2016, the content of which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present application relates to the technical field of lithium-ionbatteries and, specifically, relates to an electrolyte and a lithium-ionbattery containing the electrolyte.

BACKGROUND

In recent years, with the development of intelligent electronicproducts, there is an increasingly higher demand on battery life of thelithium-ion battery. In order to increase the energy density of thelithium-ion battery, an effective manner is to develop high-voltagelithium-ion batteries.

At present, the lithium-ion battery with a working voltage is ≧4.4V hasbecome a research hotspot for various R&D institutions and companies.However, when at high voltage, the positive electrode material will hasimproved oxidation activity and reduced stability, resulting in that theelectrochemical oxidizing reaction of the non-aqueous electrolyte willreadily occur on the surface of the positive electrode, and thus theelectrolyte will decompose and generate gas. At the same time, reductionreaction will occur to the transition metal elements in the positiveelectrode material, such as nickel, cobalt, manganese and so on, andthus such transition metal elements will precipitate out, which willcause further deterioration of electrochemical performance of thelithium-ion battery. A primary solution at present is to add into theelectrolyte a film forming additive which can form a film at thepositive electrode, which, however, will increase interface impedance,and thus reduce transport and diffusion kinetic performance of lithiumions in the battery and therefore cause deterioration of rate and cycleperformance of the battery. Chainlike carbonate dimers, chainlikecarboxylate dimers, chainlike sulfonate dimers or phosphate esters canimprove high-temperature storage performance, initial charge/dischargeperformance, safety and cycle performance, etc., however, it isdifficult for these materials to wet the electrode plate and separatoras a result of too large viscosities thereof, which therefore,especially under high compact density, causes disadvantageous effects tothe cycle performance, rate performance and low-temperature performanceof the cell.

With respect to the defects of the prior art, the present application isproposed.

SUMMARY

A primary invention object of the present application is to provide anelectrolyte.

A secondary invention object of the present application is to provide alithium-ion cell containing the electrolyte.

In order to accomplish the objects of the present application, theadopted technical solutions include:

The present application relates to an electrolyte, including a lithiumsalt, an organic solvent and additives, characterized in that, theadditives comprise additive A and additive B, wherein the additive A isselected from a group consisting of carbonate dimers, carboxylatedimers, sultone dimers and combinations thereof, and the additive B isselected from a group consisting of fluoroethers and combinationsthereof;

the additive A preferably includes a carbonate dimer and/or acarboxylate dimer and a sultone dimer.

Preferably, a structural formula of the carbonate dimer is shown asFormula I:

in Formula I, R₁₁ and R₁₃ are respectively selected from a groupconsisting of substituted or unsubstituted C_(1˜12) alkyls, substitutedor unsubstituted C_(2˜12) alkenyls, substituted or unsubstitutedC_(2˜12) alkynyls, substituted or unsubstituted C_(6˜26) aryls andsubstituted or unsubstituted C_(5˜22) heteroaryls, wherein eachsubstituting group is selected from a group consisting of halogens,C_(6˜26) aryls and C_(3˜8) cyclic alkyls;

R₁₂ is selected from a group consisting of substituted or unsubstitutedC_(1˜12) alkylenes, substituted or unsubstituted C_(6˜26) arylenes andradical groups composed of at least one ether bond and at least onesubstituted or unsubstituted C_(1˜12) alkylene, wherein eachsubstituting group is selected from a group consisting of halogens.

Preferably, a structural formula of the carboxylate dimer is shown asFormula II:

in Formula II, R₂₁ and R₂₃ are respectively selected from a groupconsisting of substituted or unsubstituted C_(1˜12) alkyls, substitutedor unsubstituted C_(2˜12) alkenyls, substituted or unsubstitutedC_(2˜12) alkynyls, substituted or unsubstituted C_(6˜26) aryls andsubstituted or unsubstituted C_(5˜22) heteroaryls, wherein eachsubstituting group is selected from a group consisting of halogens,C_(6˜26) aryls and C_(3˜8) cyclic alkyls;

R₂₂ is selected from a group consisting of substituted or unsubstitutedC_(1˜12) alkylenes, substituted or unsubstituted C_(6˜26) arylenes andradical groups composed of at least one ether bond and at least onesubstituted or unsubstituted C_(1˜12) alkylene, wherein eachsubstituting group is selected from a group consisting of halogens.

Preferably, a structural formula of the sultone dimer is shown asFormula III:

in Formula III, R₃₁ and R₃₃ are respectively selected from a groupconsisting of substituted or unsubstituted C_(1˜12) alkyls, substitutedor unsubstituted C_(2˜12) alkenyls, substituted or unsubstitutedC_(2˜12) alkynyls, substituted or unsubstituted C_(6˜26) aryls andsubstituted or unsubstituted C_(5˜22) heteroaryls, wherein eachsubstituting group is selected from a group consisting of halogens,C_(6˜26) aryls and C_(3˜8) cyclic alkyls;

R₃₂ is selected from a group consisting of substituted or unsubstitutedC_(1˜12) alkylenes, substituted or unsubstituted C_(6˜26) arylenes andradical groups composed of at least one ether bond and at least onesubstituted or unsubstituted C_(1˜12) alkylene, wherein eachsubstituting group is selected from a group consisting of halogens.

Preferably, a structural formula of the fluoroether compound is shown asFormula IV:

R₄₁—O—R₄₂   (IV)

in Formula IV, R₄₁ and R₄₂ are respectively selected from a groupconsisting of C_(1˜20) alkyls and C_(1˜20) fluoroalkyls; at least one ofR₄₁ and R₄₂ is a C_(1˜20) fluoroalkyl; and the fluoroalkyl is an alkylof which all or partial hydrogen atoms are substituted by a fluorine;

R₄₁ and R₄₂ are preferably selected from a group consisting of C_(1˜9)alkyls and C_(1˜9) fluoroalkyls, respectively.

Preferably, the fluoroether compound is selected from a group consistingof CF₃OCH₃, CF₃OC₂H₆, F(CF₂)₂OCH₃, F(CF₂)₂OC₂H₅, F(CF₂)₃OCH₃,F(CF₂)₃OC₂H₅, F(CF₂)₄OCH₃, F(CF₂)₄OC₂H₅, F(CF₂)₅OCH₃, F(CF₂)₅OC₂H₅,F(CF₂)₈OCH₃, F(CF₂)₈OC₂H₅, F(CF₂)₉OCH₃, CF₃CH₂OCH₃, CF₃CH₂OCHF₂,CF₃CF₂CH₂OCH₃, CF₃CF₂CH₂OCHF₂, CF₃CF₂CH₂O(CF₂)₂H, CF₃CF₂CH₂O(CF₂)₂F,HCF₂CH₂OCH₃, H(CF₂)₂OCH₂CH₃, H(CF₂)₂OCH₂CF₃, H(CF₂)₂CH₂OCHF₂,H(CF₂)₂CH₂O(CF₂)₂H, H(CF₂)₂CH₂O(CF₂)₃H, H(CF₂)₃CH₂O(CF₂)₂H,(CF₃)₂CHOCH₃, (CF₃)₂CHCF₂OCH₃, CF₃CHFCF₂OCH₃, CF₃CHFCF₂OCH₂CH₃,CF₃CHFCF₂CH₂OCHF₂ and combinations thereof.

Preferably, a total content of the additive A and the additive B is0.001%˜30% by weight of the electrolyte.

Preferably, the additives further include additive C selected from agroup consisting of nitrile compounds, cyclic ester compounds containinga sulfur-oxygen double bond, cyclic carbonate compounds, compoundscontaining a carbon-nitrogen double bond and combinations thereof;

the nitrile compound is selected from a group consisting of alkanescontaining 1˜5 nitrile groupings, olefins containing 1˜5 nitrilegroupings and combinations thereof;

the cyclic ether compound containing a sulfur-oxygen double bond isselected from a group consisting of cyclic sulfates, cyclic sulfites,sultones and combinations thereof;

the compound containing a carbon-nitrogen double bond is selected from agroup consisting of compounds containing

and —N═C═N— and combinations thereof.

Preferably, the nitrile compound is selected from a group consisting ofC_(2˜12) alkanes containing 1˜4 nitrile groupings, C_(2˜12) olefinscontaining 1˜4 nitrile groupings and combinations thereof;

the cyclic ether compound containing a sulfur-oxygen double bond isselected from a group consisting of compounds shown as Formula V1,compounds shown as Formula V2, compounds shown as Formula V3 andcombinations thereof; the cyclic carbonate compound is selected fromcompounds shown as Formula V4 and combinations thereof;

R₅₁, R₅₂, R₅₃ and R₅₄ are respectively selected from a group consistingof substituted or unsubstituted C_(1˜4) alkylenes and substituted orunsubstituted C_(2˜4) alkenylenes, wherein each substituting group isselected from a group consisting of halogens and C_(2˜4) alkenyls.

Preferably, the additive C is selected from a group consisting ofacetonitrile, propionitrile, butyronitrile, valeronitrile,butenenitrile, 2-methyl-3-butenenitrile, malononitrile, succinonitrile,glutaronitrile, hexanedinitrile, fumarodinitrile, 1,2-ethylene sulfate,1,3-propylene sulfate, 1,3-propylene sulfite, 1,3-propane sultone,1,4-butane sultone, prop-1-ene-1,3-sultone, vinylene carbonate,fluoroethylene carbonate, fluorovinylene carbonate, 1,2-difluorovinylenecarbonate, vinyl ethylene carbonate, dicyclohexylcarbodiimide andcombinations thereof;

a content of the additive C is preferably 0.01%˜10% by weight of theelectrolyte.

The present application further relates to a lithium-ion batteryincluding a positive electrode plate containing a positive electrodeactive material, a negative electrode plate containing a negativeelectrode active material, a separator for lithium battery and theelectrolyte according to the present application.

The technical solutions of the present application can have at least thefollowing beneficial effects:

In the present application, the fluoroethers contained in theelectrolyte firstly play a role of surfactants which prompt the wettingof the ester dimers on the electrode plate and separator, so as tocompensate for the insufficient wetting ability of the ester dimers as aresult of large viscosities thereof. Strong hydrogen bonding interactionreadily occurs between a plurality of O═X (X is carbon or sulfur)radical groups of the ester dimers and the fluoroether, which helps thefluoroether form a stable and compact protection film. Due to strongelectron pulling effect of the fluorine atom of the fluoroether, theester dimer will also readily form a film on the negative electrodesurface. As a function of the hydrogen bonding interaction between theO═X radical groups in the ester dimer and the fluoroether, theprotection film is stable at high temperature or high voltage and willnot decompose during cycling. The lithium battery of the presentapplication can realize the object of high voltage, of which the highestnormal working voltage can be improved to 4.4˜5.0V, and the lithiumbattery has good cycle performance, higher capacity retention rate atcharge/discharge and improved service life.

The present application is further explained in connection with thefollowing embodiments. It is appreciated that these embodiments aremerely used to illustrate the present application but not to limit thescope of the present application.

DESCRIPTION OF EMBODIMENTS

The present application proposes an electrolyte, including a lithiumsalt, an organic solvent and additives, characterized in that, theadditives include additive A and additive B, wherein the additive A isselected from a group consisting of carbonate dimers, carboxylatedimers, sultone dimers and combinations thereof, and the additive B isselected from a group consisting of fluoroethers and combinationsthereof.

As an improvement to the electrolyte of the present application, theadditive A includes a carbonate dimer and/or a carboxylate dimer and asultone dimer.

As an improvement to the electrolyte of the present application, astructure of the carbonate dimer is shown as Formula I:

in Formula I, R₁₁ and R₁₃ are respectively selected from a groupconsisting of substituted or unsubstituted C_(1˜12) alkyls, substitutedor unsubstituted C_(2˜12) alkenyls, substituted or unsubstitutedC_(2˜12) alkynyls, substituted or unsubstituted C_(6˜26) aryls andsubstituted or unsubstituted C_(5˜22) heteroaryls, wherein eachsubstituting group is selected from a group consisting of halogens,C_(6˜26) aryls and C_(3˜8) cyclic alkyls,

R₁₂ is selected from a group consisting of substituted or unsubstitutedC_(1˜12) alkylenes, substituted or unsubstituted C_(6˜26) arylenes andradical groups composed of at least one ether bond and at least onesubstituted or unsubstituted C_(1˜12) alkylene, wherein eachsubstituting group is selected from a group consisting of halogens.

As an improvement to the electrolyte of the present application, R₁₁ andR₁₃ are respectively selected from a group consisting of C_(1˜6) alkyls;and R₁₂ is selected from a group consisting of C_(1˜6) alkylenes.

As an improvement to the electrolyte of the present application, partialexamples of the carbonate dimer are as follows:

As an improvement to the electrolyte of the present application, astructure of the carboxylate dimer is shown as Formula II:

in Formula II, R₂₁ and R₂₃ are respectively selected from a groupconsisting of substituted or unsubstituted C_(1˜12) alkyls, substitutedor unsubstituted C_(2˜12) alkenyls, substituted or unsubstitutedC_(2˜12) alkynyls, substituted or unsubstituted C_(6˜26) aryls andsubstituted or unsubstituted C_(5˜22) heteroaryls, wherein eachsubstituting group is selected from a group consisting of halogens,C_(6˜26) aryls and C_(3˜8) cyclic alkyls;

R₂₂ is selected from a group consisting of substituted or unsubstitutedC_(1˜12) alkylenes, substituted or unsubstituted C_(6˜26) arylenes andradical groups composed of at least one ether bond and at least onesubstituted or unsubstituted C_(1˜12) alkylene, wherein eachsubstituting group is selected from a group consisting of halogens.

As an improvement to the electrolyte of the present application, R₂₁ andR₂₃ are respectively selected from a group consisting of C_(1˜6) alkyls;R₂₂ is selected from a group consisting of C_(1˜12) alkylenes anddivalent radical groups obtained by connecting a ether bond with twoC_(1˜6) alkylenes.

As an improvement to the electrolyte of the present application, partialexamples of the carboxylate dimer are as follows:

As an improvement to the electrolyte of the present application, astructure of the sultone dimer is shown as Formula III:

in Formula III, R₃₁ and R₃₃ are respectively selected from a groupconsisting of substituted or unsubstituted C_(1˜12) alkyls, substitutedor unsubstituted C_(2˜12) alkenyls, substituted or unsubstitutedC_(2˜12) alkynyls, substituted or unsubstituted C_(6˜26) aryls andsubstituted or unsubstituted C_(5˜22) heteroaryls, wherein eachsubstituting group is selected from a group consisting of halogens,C_(6˜26) aryls and C_(3˜8) cyclic alkyls;

R₃₂ is selected from a group consisting of substituted or unsubstitutedC_(1˜12) alkylenes, substituted or unsubstituted C_(6˜26) arylenes andradical groups composed of at least one ether bond and at least onesubstituted or unsubstituted C_(1˜12) alkylene, wherein eachsubstituting group is selected from a group consisting of halogens.

As an improvement to the electrolyte of the present application, R₃₁ andR₃₃ are respectively selected from a group consisting of C_(1˜6) alkyls;and R₃₂ is selected from a group consisting of C_(1˜6) alkylenes.

As an improvement to the electrolyte of the present application, partialexamples of the sultone dimer are as follows:

As an improvement to the electrolyte of the present application, astructure of the fluoroether compound is shown as Formula IV:

R₄₁—O—R₄₂   (IV)

in Formula IV, R₄₁ and R₄₂ are respectively selected from a groupconsisting of C_(1˜20) alkyls and C_(1˜20) fluoroalkyls; at least one ofR₄₁ and R₄₂ is a C_(1˜20) fluoroalkyl; and the fluoroalkyl is an alkylof which all or partial hydrogen atoms are substituted by fluorine;

As an improvement to the electrolyte of the present application, R₄₁ andR₄₂ are respectively selected from a group consisting of C_(1˜9) alkylsand C_(1˜9) fluoroalkyls.

As an improvement to the electrolyte of the present application, thefluoroether compound is selected from a group consisting of CF₃OCH₃,CF₃OC₂H₆, F(CF₂)₂OCH₃, F(CF₂)₂OC₂H₅, F(CF₂)₃OCH₃, F(CF₂)₃OC₂H₅,F(CF₂)₄OCH₃, F(CF₂)₄OC₂H₅, F(CF₂)₅OCH₃, F(CF₂)₅OC₂H₅, F(CF₂)₈OCH₃,F(CF₂)₈OC₂H₅, F(CF₂)₉OCH₃, CF₃CH₂OCH₃, CF₃CH₂OCHF₂, CF₃CF₂CH₂OCH₃,CF₃CF₂CH₂OCHF₂, CF₃CF₂CH₂O(CF₂)₂H, CF₃CF₂CH₂O(CF₂)₂F, HCF₂CH₂OCH₃,H(CF₂)₂OCH₂CH₃, H(CF₂)₂OCH₂CF₃, H(CF₂)₂CH₂OCHF₂, H(CF₂)₂CH₂O(CF₂)₂H,H(CF₂)₂CH₂O(CF₂)₃H, H(CF₂)₃CH₂O(CF₂)₂H, (CF₃)₂CHOCH₃, (CF₃)₂CHCF₂OCH₃,CF₃CHFCF₂OCH₃, CF₃CHFCF₂OCH₂CH₃, CF₃CHFCF₂CH₂OCHF₂ and combinationsthereof.

As an improvement to the electrolyte of the present application, thefluoroether compound is selected from a group consisting of F(CF₂)₃OCH₃,H(CF₂)₂CH₂O(CF₂)₂H and CF₃CHFCF₂CH₂OCHF₂.

As an improvement to the electrolyte of the present application, a totalcontent of the additive A and the additive B is 0.001%˜30% by weight ofthe electrolyte. It is found upon researches that, when the content ofthe composite additives in the electrolyte is less than 0.001%, theelectrolyte cannot effectively form a stable passive film, such that thelow-temperature performance and rate performance of the lithium-ionbattery cannot be basically improved; when the content of the compositeadditives in the electrolyte is more than 30%, a relatively thick filmis formed, which therefore increases the impedance and reduces the cycleperformance of the lithium-ion battery.

As an improvement to the electrolyte of the present application, thetotal content of the additive A and the additive B is 1˜20% by weight ofthe electrolyte. The content ratio of the ester dimer compound and thefluoroether compound in the composite additives is not limited.

In the present application, the ester dimer can be obtained by aconventional synthetic method, for example the method disclosed inCN200810107928, or commercially purchased; the fluoroether can becommercially available and its original source is not limited.

As an improvement to the electrolyte of the present application, theadditives further include additive C selected from a group consisting ofnitrile compounds, cyclic ester compounds containing a sulfur-oxygendouble bond, cyclic carbonate compounds, compounds containing acarbon-nitrogen double bond and combinations thereof. When the additivesinclude the additive C, the cycle performance of the lithium-ion batterycan be further improved, for example, the lithium-ion battery can haverelatively high capacity retention rate after a plurality of cycles at ahigh voltage≧4.45V. Moreover, the rate performance and the dischargeperformance of the battery at low temperature can also be furtherimproved.

As an improvement to the electrolyte of the present application, acontent of the additive C is 0.01%˜10% by weight of the electrolyte.

In the above-mentioned additive C, the number of the nitrile grouping inthe nitrile compound may be 1, 2, 3, 4 or 5; and the nitrile compound isan alkane containing 1˜5 nitrile groupings or an olefin containing 1˜5nitrile groupings, preferably a C_(2˜12) alkane containing 1˜4 nitrilegroupings or a C_(2˜12) olefin containing 1˜4 nitrile groupings.

The nitrile compound is: a mononitrile compound if it contains only onenitrile grouping, a dinitrile compound if it contains two nitrilegroupings, a trinitrile compound if it contains three nitrile groupings,or a tetranitrile compound if it contains four nitrile groupings. Inaddition, the nitrile compound may further contain a carbon-carbondouble bond. Preferably, the nitrile compound is selected from a groupconsisting of mononitrile compounds, dinitrile compounds, trinitrilecompounds, tetranitrile compounds and combinations thereof.

Examples of the nitrile compound may include mononitrile compounds suchas acetonitrile, propionitrile, butyronitrile, isobutyronitrile,valeronitrile, isovaleronitrile, 2-methyl butanenitrile,trimethylacetonitrile, hexanenitrile, cyclopentanecarbonitrile,cyclohexanecarbonitrile, acrylonitrile, methacrylonitrile,butenenitrile, 2-methyl-3-butenenitrile, 2-methyl-2-butenenitrile,2-pentenenitrile, 2-methyl-2-pentenenitrile, 3-methyl-2-pentenenitrile,2-hexenenitrile, fluoroacetonitrile, difluoroacetonitrile,trifluoroacetonitrile, 2-fluoropropanenitrile, 3-fluoropropanenitrile,2,2-difluoropropanenitrile, 2,3-difluoropropanenitrile,3,3-difluoropropanenitrile, 2,2,3-trifluoropropionitrile,3,3,3-trifluoropropionitrile and pentafluoropropionitrile; dinitrilecompounds such as malononitrile, succinonitrile,tetramethyl-succinonitrile, glutaronitrle, 2-methylglutaronitrile,hexanedinitrile, fumarodinitrile and 2-methyleneglutaronitrile;trinitrile compounds such as 1,3,5-pentanetricarbonitrile,1,2,3-propanetricarbonitrile and 1,3,6-hexanetricarbonitrile; andtetranitrile compounds such as tetracyanoethylene.

Preferably, the nitrile compound is selected from a group consisting ofacetonitrile, propionitrile, butyronitrile, valeronitrile,butenenitrile, 2-methyl-3-butenenitrile, acrylonitrile, succinonitrile,glutaronitrle, hexanedinitrile (abbreviated as ADN), fumarodinitrile andcombinations thereof; more preferably, the nitrile compound is selectedfrom a group consisting of acrylonitrile, succinonitrile, glutaronitrle,hexanedinitrile, fumarodinitrile, 1,3,6-hexanetricarbonitrile andcombinations thereof.

Preferably, a content of the nitrile compound is 0.01˜5% by weight ofthe electrolyte, more preferably 0.1˜3%.

In the abovementioned additive C, the cyclic ester compound containing asulfur-oxygen double bond may be selected from a group consisting ofcyclic sulfates, cyclic sulfites, sultones and combinations thereof,wherein the sultones include saturated sultones and sultones containingan unsaturated double bond.

The cyclic sulfate compounds are shown as Formula V1, the cyclic sulfitecompounds are shown as V3, and the sultone compounds are shown as V2:

R₅₁, R₅₂ and R₅₃ are respectively selected from a group consisting ofsubstituted or unsubstituted C_(1˜4) alkylenes and substituted orunsubstituted C_(2˜4) alkenylenes, wherein each substituting group isselected from a group consisting of halogens.

Preferably, R₅₁ and R₅₃ are respectively selected from a groupconsisting of substituted or unsubstituted C_(1˜4) alkylenes; R₅₂ isselected from a group consisting of substituted or unsubstituted C_(1˜4)alkylenes and substituted or unsubstituted C_(2˜4) alkenylenes.

Preferably, the cyclic ester compound containing a sulfur-oxygen doublebond is selected from a group consisting of the following compounds andcombinations thereof:

ethylene sulfate;

1,3-propylene sulfate;

1,3-propylene sulfite;

1,3-propanesultone (abbreviated as PS);

1,4-butane sultone;

prop-1-ene-1,3-sultone.

Preferably, a content of the cyclic ester compound containing asulfur-oxygen double bond is 0.01˜5% by weight of the electrolyte, morepreferably 0.1˜3%.

The cyclic ester compound containing a sulfur-oxygen double bond may beotherwise selected from a group consisting of the following compounds:

The cyclic carbonate compound includes saturated cyclic carbonates andcyclic carbonates containing an unsaturated carbon-carbon bond, of whichthe structural formula is shown as Formula V4:

R₅₄ is selected from a group consisting of substituted or unsubstitutedC_(1˜4) alkylenes and substituted or unsubstituted C_(2˜4) alkenylenes,wherein each substituting group is selected from a group consisting ofhalogens and C_(2˜4) alkenyls.

In the cyclic carbonate compound containing an unsaturated carbon-carbonbond, the unsaturated carbon-carbon bond is preferably a double bondwhich may be or may not be located on the ring thereof.

In the abovementioned electrolyte, the cyclic carbonate compound ispreferably selected from a group consisting of the following compoundsand combinations thereof:

vinylene carbonate (abbreviated as VC),

fluoroethylene carbonate;

fluorovinylene carbonate;

1,2-difluorovinylene carbonate;

vinyl ethylene carbonate.

Preferably, a content of the cyclic carbonate compound is 0.01˜5% byweight of the electrolyte, more preferably 0.1˜3%.

The cyclic carbonate compound may be otherwise selected from a groupconsisting of the following compounds and combinations thereof:

In the abovementioned additive C, the compound containing acarbon-carbon double bond is selected from a group consisting ofcompounds containing an imido-group, compounds containing a carbodiimidegroup and combinations thereof, wherein the imido-group is shown as

and the carbodiimide group is shown as —N═C═N—;

the compound containing a carbon-nitrogen double bond is shown asFormula VIa; and the compound containing a carbodiimide group is shownas Formula VIb;

R₆₁, R₆₂, R₆₃, R₆₄ and R₆₅ are respectively selected from a groupconsisting of substituted or unsubstituted C_(1˜12) alkyls andsubstituted or unsubstituted C_(2˜12) alkenyls, wherein eachsubstituting group is selected from a group consisting of halogens.

Examples of the compound containing a carbon-nitrogen double bond caninclude:

N-pentyl-isopropyl-imide (abbreviated as NPPI),

dicyclohexylcarbodiimide (abbreviated as DCC).

Preferably, a content of the compound containing a carbon-nitrogendouble bond is 0.01˜5% by weight of the electrolyte, more preferably0.1˜3%.

In the above-mentioned structural formulas of the present application:

The C_(1˜12) alkyl may be a chainlike alkyl or a cyclic alkyl, and ahydrogen on the ring of the cyclic alkyl can be substituted by an alkyl.A straight or branched alkyl is preferred. The lower limit value of thenumber of carbon atoms in the C_(1˜12) alkyl is preferably 2, 3, 4 or 5,and the upper limit value of the number of carbon atoms in the C_(1˜12)alkyl is preferably 3, 4, 5, 6, 8, 9, 10 or 11. It is preferred toselect a C_(1˜10) alkyl, more preferably a C_(1˜6) chainlike alkyl or aC_(3˜8) cyclic alkyl, further more preferably a C_(1˜4) chainlike alkylor a C_(5˜7) cyclic alkyl. Examples of the alkyl may include: methyl,ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl,n-pentyl, iso-pentyl, neopentyl, hexyl, 2-methylpentyl, 3-methylpentyl,1,1,2-trimethylpropyl, 3,3-dimethylbutyl, heptyl, 2-heptyl, 3-heptyl,2-methylhexyl, 3-methylhexyl, iso-heptyl, octyl, nonyl and decyl.

The C_(2˜12) alkenyl may be a cyclic alkenyl or a chainlike alkenyl,preferably a straight or branched alkenyl. Further, the alkenylpreferably has only one double bond. A lower limit value of the numberof carbon atoms in the alkenyl is preferably 3, 4 or 5, and an upperlimit value of the number of carbon atoms in the alkenyl is preferably6, 8, 10 or 11. It is preferred to select a C_(2˜10) alkenyl, morepreferably a C_(2˜6) alkenyl, further more preferably a C_(2˜5) alkenyl.Examples of the alkenyl may include: vinyl, propenyl, isopropenyl,pentenyl, cyclohexenyl, cycloheptenyl and cyclo-octenyl. As for thealkynyle, it can be selected by referring to the selections of thealkenyl.

The C_(1˜12) alkylene is a straight or branched alkylene, of which alower limit value of the number of carbon atoms is preferably 1, 2, 3 or4, and an upper limit value of the number of carbon atoms is preferably6, 7, 8, 9, 10 or 11. Examples of the alkylene may include: methylene,1,2-ethylidene, 1,3-propylidene, 2-methyl-1,3-propylidene,1,3-dimethyl-propylidene, 1-methyl-1,2-ethylidene,1,1-dimethylethylidene, 1,2-dimethylethylidene, 1,4-butylidene,1,5-pentylidene, 1,6-hexylidene, 1,1,4,4-tetramethylbutylidene,cyclopropylidene, 1,2-cyclopropylidene, 1,3-cyclobutylidene,cyclobutylidene, cyclohexylidene, 1,4-cyclohexylidene,1,4-cycloheptylidene, cycloheptylidene, 1,5-cyclo-octamethylene andcyclo-octamethylene.

The C_(2˜12) alkenylene is a straight or branched alkenylene, of whichthe number and position of the double bond are not limited, which can beselected according to actual demands. In particular, the number of thedouble bond may be 1, 2, 3 or 4. In the alkenylene, a lower limit valueof the number of carbon atoms is preferably 2, 3, 4 or 5, and an upperlimit value of the number of carbon atoms is preferably 6, 8, 10 or 11.Examples of the alkenylene may include: 1,2-vinylene, vinylidene,1,3-propenylene, 2-propenylene, methyl-1,2-vinylene, ethyl-1,2-vinylene,1,4-tetramethylene-2-alkenyl, 1,5-pentamethylene-2-alkenyl,1,6-hexamethylene-3-alkenyl, 1,7-heptamethylene-3-alkenyl and1,8-octamethylene-2-alkenyl.

The C_(6˜26) aryl could be, for example a phenyl, a phenylalkyl, a arylcontaining at least one phenyl such as biphenyl and polycyclic aromaticgroup such as naphthyl, anthryl and phenanthryl, and a hydrogen of thebiphenyl and the polycyclic aromatic group can be substituted by analkyl or an alkenyl. It is preferred to select a C_(6˜16) aryl, morepreferably a C_(6˜14) aryl, and further more preferably a C_(6˜9) aryl.Examples of the aryl may include: phenyl, benzyl, biphenyl, p-tolyl,o-tolyl and m-tolyl.

The C_(5˜22) heteroaryl may include: furyl, thienyl, pyrryl, thiazolyl,imidazolyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, indolyl andquinolyl.

The halogen is selected from a group consisting of fluorine, chlorineand bromine, and is preferably selected from a group consisting offluorine and chlorine.

As an improvement of the electrolyte of the present application, theorganic solvent is particularly a non-aqueous organic solvent,preferably selected from a group consisting of compounds having 1˜8carbon atoms and at least one ester group.

Preferably, the organic solvent is selected from a group consisting ofethylene carbonate, propylene carbonate, butylene carbonate,fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate,dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate,ethyl propyl carbonate, 1,4-butyrolactone, methyl propionate, methylbutyrate, ethyl acetate, ethyl propionate, ethyl butyrate andcombinations thereof. However, the solvent is not limited to theabove-mentioned specific compounds, and the solvent may be otherwiseselected from fluoro-compounds of the above-mentioned compounds.

In the abovementioned electrolyte, the lithium salt is elected from agroup consisting of organic lithium salts, inorganic lithium salts andcombinations thereof. Particularly, the lithium salt contains at leastone element of fluorine, boron and phosphorus.

Examples of the lithium salt may include: lithium hexafluorophosphateLiPF₆, lithium difluorophosphate LiPO₂F₂, lithium tetrafluoroborateLiBF₄, lithium bis(trifluoromethanesulphonyl)imide LiN(CF₃SO₂)₂(abbreviated as LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO₂F)₂)(abbreviated as LiFSI), lithium bis(oxalate)borate LiB(C₂O₄)₂(abbreviated as LiBOB), lithium oxalyldifluoroborate LiBF₂(C₂O₄)(abbreviated as LiDFOB).

In the abovementioned electrolyte, the lithium salt is preferablyselected from a group consisting of lithium hexafluorophosphate, lithiumdifluorophosphate, lithium tetrafluoroborate, lithiumhexafluoroarsenate, lithium perchlorate, lithium trifluorosulfonate,lithium bis(trifluoromethylsulfonyl) imide, lithium bis(fluorosulfonyl)imide, lithium tris(trifluoromethylsulfonyl) methide and combinationsthereof.

Particularly, the concentration of the lithium salt can be 0.5mol/L˜3mol/L.

In the present application, the electrolyte can be prepared by aconventional manner, for example, to evenly mix all the materials in theelectrolyte.

Another object of the present application is to provide a lithium-ionbattery, including a positive electrode plate, a negative electrodeplate, a separator for lithium battery and the electrolyte of thepresent application.

In the abovementioned lithium-ion battery, the positive electrode plateincludes a positive electrode active material; the negative electrodeplate includes a negative electrode active material; and the specifictypes of the positive electrode active material and the negativeelectrode active material are not limited, which can be selectedaccording to actual demands.

Preferably, the positive electrode active material is selected from agroup consisting of lithium cobaltate (LiCoO₂), lithiumnickel-manganese-cobalt oxide, lithium ferrous phosphate (LiFePO₄),lithium manganate (LiMn₂O₄) and combinations thereof.

Preferably, the negative electrode active material is carbon and/orsilicon, for example, natural graphite, artificial graphite, mesocarbonmicrobeads (abbreviated as MCMB), hard carbon, soft carbon, silicon,silicon-carbon composites, Li—Sn alloy, Li—Sn—O alloy, Sn, SnO, SnO₂,lithiated TiO₂—Li₄Ti₅O₁₂ with a spinel structure and Li—Al alloy are allsuitable as the negative electrode active material.

The present application is further described in connection with thefollowing embodiments. It should be noted that, these embodiments aremerely exemplary, which do not constitute any limit to the protectionscope of the present application.

In the following embodiments, comparative examples and test examples,all used reagents, materials and instruments could be commerciallyavailable unless otherwise noted, and the used reagents can also beobtained by conventional manners.

Embodiments 1˜15

In the following embodiments, comparative examples and test examples,the used materials are listed as follows

Organic solvent: ethylene carbonate (EC), propylene carbonate (PC),diethyl carbonate (DEC); Lithium salt: LiPF₆;

Additive A: Ester Dimers;

Carbonate dimer: 2-ethoxycarbonyloxyethyl ethyl carbonate (AN1);

Carboxylate dimer: diethylene glycol diacetate (AN2);

Sultone dimer: 4-methansulfonyloxy-butyl methanesulfonate (AN3)

Additive B: Fluoroether:

F(CF₂)₃OCH₃   (AM1);

CF₃CHFCF₂CH₂OCHF₂   (AM2);

H(CF₂)₂CH₂O(CF₂)₂H   (AM3);

Additive C:

fluoroethylene carbonate (FEC);

vinylene carbonate (VC);

1,3-propanesultone (PS);

hexanedinitrile (ADN);

Separator for lithium battery: polypropylene separator membrane with athickness of 16 μm (Model: A273, provided by Celgard Corporation).

Lithium batteries (hereinafter referred to as batteries) 1˜15 are allprepared according to the following manner:

(1) Preparation of Positive Electrode Plate

Lithium cobaltate (LiCoO₂), a binder (polyvinylidene fluoride) and aconductive agent (acetylene black) are mixed in a weight ratio ofLiCoO₂: polyvinylidene fluoride: acetylene black=96:2:2, then added withN-methylpyrrolidone (NMP) and stirred by a vacuum mixer to form auniform and transparent state, so as to obtain a positive electrodeslurry; the positive electrode slurry is then evenly coated onto analumunium foil with a thickness of 12 μm, dried at room temperature andthen dried in an oven at 120° C. for 1 hour, then cold-pressed and slit,so as to obtain a positive electrode plate.

(2) Preparation of Negative Electrode Plate

Graphite, acetylene black, sodium carboxymethylcellulose (CMC) thickenerand styrene-butadiene rubber binder are mixed in a weight ratio ofgraphite: acetylene black: styrene-butadiene rubber binder: sodiumcarboxymethylcellulose thickener=95:2:2:1, then added with deionizedwater and stirred by a vacuum mixer, so as to form a negative electrodeslurry; the negative electrode slurry is then evenly coated onto acopper foil, dried at room temperature and then dried in an oven at 120°C. for 1 hour, then cold-pressed and slit, so as to obtain a negativeelectrode plate.

(3) Preparation of Electrolyte

Electrolytes 1˜15 are prepared according to the following manner:

In a glove box filled with argon atmosphere with a moisture content<10ppm, EC, PC and DEC are evenly mixed in a weight ratio of 1:1:1 so as toform an organic solvent; the lithium salt which has been fully dried isthen dissolved into the abovementioned organic solvent; the additive A(AN1, AN2, AN3, AM1, AM2, AM3) and additive B (FEC, VC, PS, ADN, EDN)are then added into the organic solvent according to the content shownin Table 1 and evenly mixed, so as to obtain an electrolyte, of whichthe concentration of the lithium salt is 1 mol/L, and the weight ratioof EC, PC and DEC is EC: PC: DEC=1:1:2.

(4) Preparation of Lithium-Ion Battery

The positive electrode plate, separator for lithium battery and negativeelectrode plate are stacked in sequence and then winded to form a barecell, such that the separator can insulate the positive electrode platefrom the negative electrode plate; the bare cell is then packaged intoan external packaging foil, then injected with the prepared electrolyte,vacuum sealed, let standby, formed and shaped, so as to obtain abattery.

During the preparation of the abovementioned batteries, the selectedelectrolyte in each battery and the specific type and contents of theused additive A and additive B in each electrolyte are shown in Table 2.

In Table 1, the content of the additive is a weight percentage countedbased on the total weight of the electrolyte.

TABLE 1 Relevant parameters of additives of electrolytes in Comparativeexamples 1~8 and Embodiments 1~15 Content (%) of additive in electrolyteAdditive A Additive B Additive C AN1 AN2 AN3 AM1 AM2 AM3 PS VC ADN FECEmbodiment 0.01 — — — 0.1 — — — — — 1 Embodiment 1 — — 2 — — — — — — 2Embodiment 1 — — — 2 — 2 1 — — 3 Embodiment 1 — — — — 2 2 1 — — 4Embodiment 5 — — — 10 — 2 1 — — 5 Embodiment 8 — — — — 2 2 1 — — 6Embodiment — 5 — — — 10 2 1 — — 7 Embodiment — 5 — — — 10 2 1 1 1 8Embodiment 10 — — — — 10 2 1 1 1 9 Embodiment — — 15 — — 15 3 1 1 1 10Embodiment — — 20 — — 15 3 2 2 1 11 Embodiment 5 — 5 — — 2 — — — — 12Embodiment 5 — 5 — — 2 2 1 — — 13 Embodiment — 5 5 — — 2 — — — — 14Embodiment — 5 5 — — 2 2 1 — — 15 Comparative — — — — — — — — — —example 1 Comparative — — — — — — 2 1 — — example 2 Comparative — — — —— 2 2 1 — — example 3 Comparative — — 2 — — — 2 1 — — example 4Comparative 2 — — — — — — — — — example 5 Comparative — — — — — 2 — — —— example 6 Comparative 0.01 — — — — — — — — — example 7 Comparative 20— — 20 — — — — — — example 8

Performance Test Manners:

(1) Test for Cycle Performance of Battery

At 45° C., the lithium-ion batteries of Embodiments 1-15 and Comparativeexamples 1-8 are charged with a constant current at a rate of 0.5 C to4.45V, then charged with a constant voltage to a current of 0.05 C, thendischarged with a constant current of 0.5 C to 3.0V, then repeat thecharge and discharge as above and respectively calculate the capacityretention rates after 50 cycles, 100 cycles and 300 cycles.

Capacity retention rate after n cycles=(discharge capacity after then^(th) cycle/discharge capacity after the first cycle)×100%. Relevantdata is shown in Table 2.

(2) Test for high-temperature storage performance of battery

The following test is conducted to each of the batteries obtained inEmbodiments 1˜15 and Comparative examples 1˜8:

At 25° C., a battery is charged with a constant current of 0.5 C to4.45V, charged with a constant voltage of 4.45V to a current of 0.025 Cand let to be in a fully charged state when the measured thickness isthe thickness before storage; then, the battery is respectively storedat 85° C. for 4 hours and 60° C. for 30 days, the thicknesses of thebattery after storage are respectively measured, and the thicknessexpansion rate of the battery after storage at different conditions arecalculated in the following formula. The thicknesses of the batteriesafter storage at different conditions are shown in Table 2.

Thickness expansion rate of battery=[(thickness before storage−thicknessafter storage)/thickness before storage]×100%

TABLE 2 Testing results of relevant performance of Embodiments 1~15 andComparative examples 1~8 Thickness expansion rate (%) After After Cycleperformance storage at storage at 50 100 300 85° C. for 60° C. forcycles cycles cycles 4 hours 30 days Embodiment 80.9 75.6 71.8 9.3 6.4 1Embodiment 86.9 83.5 82.5 9.7 12.1 2 Embodiment 94.7 94.2 89.5 8.1 6.7 3Embodiment 89.7 89.2 84.5 6.7 7.9 4 Embodiment 87.5 82.9 81.2 7.8 9.15 5Embodiment 93 90.1 85.9 5.6 7.3 6 Embodiment 88.4 87.6 85.2 5.4 6.9 7Embodiment 96.3 94.9 91.7 4.3 6.2 8 Embodiment 95.1 93.5 91.5 4.5 6.4 9Embodiment 93.5 91.3 88.8 3.8 6.1 10 Embodiment 93.1 90.3 87.4 4.9 7.511 Embodiment 96.7 95.2 93.2 3.2 4.6 12 Embodiment 97.3 96.1 92.9 2.94.3 13 Embodiment 97.1 95.9 93.6 2.9 4.7 14 Embodiment 97.8 96.8 94.22.2 4.5 15 Comparative 45.1 39.4 35.2 32.8 39.1 example 1 Comparative57.2 53.5 46.3 27.9 35.3 example 2 Comparative 59.5 54.8 48.7 25.3 31.2example 3 Comparative 64.2 58.2 50 24.1 30.6 example 4 Comparative 6759.65 49.4 18.5 26.7 example 5 Comparative 72 66.7 62.55 16.2 21.5example 6 Comparative 46.1 40.2 36.1 30.3 38.5 example 7 Comparative54.3 51.2 45.6 28.1 31.2 example 8

(3) Hot-Box Test

The following test is conducted to each of the batteries obtained inEmbodiments 1˜15 and Comparative examples 1˜8:

1) charging the battery with a constant current of 1.0 C to 4.45V, thencharging with a constant voltage until the current reduces to 0.05 C,and then stop charging.

2) placing the battery in a hot box, increasing the temperature from 25°C. to 150° C. at a heating rate of 5° C./min, maintaining thetemperature at 150° C. and begin timing, 1 hour later, observing thestate of the battery; the standard for passing the test includes nofuming, no fire and no explosion, and each group has 5 batteries. Theresult of hot-box test for each battery is shown in Table 4.

The safety performance of the battery is characterized by the abovehot-box test.

TABLE 3 Testing results of relevant performance of Embodiments 1~15 andComparative examples 1~8 Battery No. State after hot-box test EmbodimentAll 5 batteries pass the test with no fume, 1 no fire and no explosionEmbodiment 4 batteries pass the test and the other 2 1 battery is onfire Embodiment All 5 batteries pass the test with no fume, 3 no fireand no explosion Embodiment All 5 batteries pass the test with no fume,4 no fire and no explosion Embodiment All 5 batteries pass the test withno fume, 5 no fire and no explosion Embodiment All 5 batteries pass thetest with no fume, 6 no fire and no explosion Embodiment All 5 batteriespass the test with no fume, 7 no fire and no explosion Embodiment All 5batteries pass the test with no fume, 8 no fire and no explosionEmbodiment All 5 batteries pass the test with no fume, 9 no fire and noexplosion Embodiment All 5 batteries pass the test with no fume, 10 nofire and no explosion Embodiment All 5 batteries pass the test with nofume, 11 no fire and no explosion Embodiment All 5 batteries pass thetest with no fume, 12 no fire and no explosion Embodiment All 5batteries pass the test with no fume, 13 no fire and no explosionEmbodiment All 5 batteries pass the test with no fume, 14 no fire and noexplosion Embodiment All 5 batteries pass the test with no fume, 15 nofire and no explosion Comparative All 5 batteries are on fire example 1Comparative All 5 batteries are on fire example 2 Comparative 1 batterypasses the test and the other example 3 4 batteries are on fireComparative 1 battery passes the test and the other example 4 4batteries are on fire Comparative 2 batteries pass the test and theother example 5 3 batteries are on fire Comparative 2 batteries pass thetest and the other example 6 3 batteries are on fire Comparative 2batteries pass the test and the other example 7 3 batteries are on fireComparative 2 batteries pass the test and the other example 8 3batteries are on fire

It can be known from the relevant data in Tables 2˜4 that, inComparative examples 1˜8, Comparative examples 3˜6 containing only oneof carbonate dimer and fluoroether of the additive A have reducedcapacity retention rate and reduced rate performance due to relativelyhigh impedance during the formation of the film. However, Embodiments1˜11 adopt the combination of ester dimer and fluoroether compound,which can reduce the thickness of the SEI film on the positive electrodesurface and reduce the impedance, and improve uniformity and stabilityof the SEI film formed on the positive electrode surface, so as toimprove the rate performance and low-temperature discharge performanceof the lithium-ion battery. Such effect is particularly significant inEmbodiments 12˜14 which adopt a combination of carbonate dimer orcarboxylate dimer and sultone dimmer, since the formed complex SEI filmhas a stable structure and thus has good stability during cycling, andwill not readily be decomposed and re-formed repeatedly during cycling.The batteries of Embodiments 1˜15 perform better than the batteries ofComparative examples 1˜8 in capacity retention rate, rate performance,low-temperature discharge performance and safety performance aftercycling at 45° C.

The lithium-ion battery will have further improved cycle performance ifthe additives further include the additive C, for example, thelithium-ion battery has relatively high capacity retention rate after aplurality of cycles at a voltage≧4.45V, and further improved rateperformance and low-temperature discharge performance.

Embodiments 16˜22

Electrolytes and lithium-ion batteries are prepared according to themanner of Embodiment 1, except that the components of the additives inthe electrolytes are shown in Table 4:

TABLE 4 Electrolyte Type and content (%) of additive No. Additive AAdditive B Additive C Electrolyte 16

F(CF₂)₂OC₂H₅ 2% FEC 1% + VC 1% Electrolyte 17

F(CF₂)₄OC₂H₅ 2% FEC 1% + PS 1% Electrolyte 18

F(CF₂)₃OCH₃ 2% ADN 1% + PS 1% + VC 1% Electrolyte 19

F(CF₂)₉OCH₃ 2% FEC 1% + ADN 1% + PS 1% Electrolyte 20

CF₃CH₂OCH₃ 2% ADN 1% + PS 1% + VC 1% Electrolyte 21

CF₃CH₂OCHF₂ 2% FEC 1% + ADN 1% + PS 1% Electrolyte 22

(CF₃)₂CHCF₂OCH₃ 2% FEC 1% + ADN 1%

The lithium-ion batteries are prepared by adopting the electrolytes inTable 4 and the prepared batteries have similar properties withEmbodiment 1, which will not be repeated herein.

According to the disclosure above, those skilled in the art can makeappropriate variations and modifications to the embodiments above. Thus,the present application is not limited to the embodiments as disclosedand descried above, and the variations and modifications made to thepresent application shall also fall into the protection scope of theclaims of the present application.

What is claimed is:
 1. An electrolyte, comprising a lithium salt, anorganic solvent and additives, the additives comprise additive A andadditive B, wherein the additive A is selected from a group consistingof carbonate dimers, carboxylate dimers, sultone dimers and combinationsthereof, and the additive B is selected from a group consisting offluoroethers and combinations thereof; the additive A preferablycomprises a carbonate dimer and/or a carboxylate dimer and a sultonedimer.
 2. The electrolyte according to claim 1, wherein a structuralformula of the carbonate dimer is shown as Formula I, and a structuralformula of the carboxylate dimer is shown as Formula II;

in Formula I, R₁₁ and R₁₃ are respectively selected from a groupconsisting of substituted or unsubstituted C_(1˜12) alkyls, substitutedor unsubstituted C_(2˜12) alkenyls, substituted or unsubstitutedC_(2˜12) alkynyls, substituted or unsubstituted C_(6˜26) aryls andsubstituted or unsubstituted C_(5˜22) heteroaryls, wherein eachsubstituting group is selected from a group consisting of halogens,C_(6˜26) aryls and C_(3˜8) cyclic alkyls; R₁₂ is selected from a groupconsisting of substituted or unsubstituted C_(1˜12) alkylenes,substituted or unsubstituted C_(6˜26) arylenes and radical groupscomposed of at least one ether bond and at least one substituted orunsubstituted C_(1˜12) alkylene, wherein each substituting group isselected from a group consisting of halogens; in Formula II, R₂₁ and R₂₃are respectively selected from a group consisting of substituted orunsubstituted C_(1˜12) alkyls, substituted or unsubstituted C_(2˜12)alkenyls, substituted or unsubstituted C_(2˜12) alkynyls, substituted orunsubstituted C_(6˜26) aryls and substituted or unsubstituted C_(5˜22)heteroaryls, wherein each substituting group is selected from a groupconsisting of halogens, C_(6˜26) aryls and C_(3˜8) cyclic alkyls; R₂₂ isselected from a group consisting of substituted or unsubstitutedC_(1˜12) alkylenes, substituted or unsubstituted C_(6˜26) arylenes andradical groups composed of at least one ether bond and at least onesubstituted or unsubstituted C_(1˜12) alkylene, wherein eachsubstituting group is selected from a group consisting of halogens. 3.The electrolyte according to claim 1, wherein a structural formula ofthe sultone dimer is shown as Formula III:

in Formula III, R₃₁ and R₃₃ are respectively selected from a groupconsisting of substituted or unsubstituted C_(1˜12) alkyls, substitutedor unsubstituted C_(2˜12) alkenyls, substituted or unsubstitutedC_(2˜12) alkynyls, substituted or unsubstituted C_(6˜26) aryls andsubstituted or unsubstituted C_(5˜22) heteroaryls, wherein eachsubstituting group is selected from a group consisting of halogens,C_(6˜26) aryls and C_(3˜8) cyclic alkyls; R₃₂ is selected from a groupconsisting of substituted or unsubstituted C_(1˜12) alkylenes,substituted or unsubstituted C_(6˜26) arylenes and radical groupscomposed of at least one ether bond and at least one substituted orunsubstituted C_(1˜12) alkylene, wherein each substituting group isselected from a group consisting of halogens.
 4. The electrolyteaccording to claim 1, wherein a structural formula of the fluoroethercompound is shown as Formula IV:R₄₁—O—R₄₂   (IV) in Formula IV, R₄₁ and R₄₂ are respectively selectedfrom a group consisting of C_(1˜20) alkyls and C_(1˜20) fluoroalkyls; atleast one of R₄₁ and R₄₂ is a C_(1˜20) fluoroalkyl; and the fluoroalkylis an alkyl of which all or partial hydrogen atoms are substituted byfluorine; R₄₁ and R₄₂ are preferably selected from a group consisting ofC_(1˜9) alkyls and C_(1˜9) fluoroalkyls, respectively.
 5. Theelectrolyte according to claim 4, wherein the fluoroether compound isselected from a group consisting of CF₃OCH₃, CF₃OC₂H₆, F(CF₂)₂0CH₃,F(CF₂)₂OC₂H₅, F(CF₂)₃OCH₃, F(CF₂)₃OC₂H₅, F(CF₂)₄OCH₃, F(CF₂)₄OC₂H₅,F(CF₂)₅OCH₃, F(CF₂)₅OC₂H₅, F(CF₂)₈OCH₃, F(CF₂)₈OC₂H₅, F(CF₂)₉OCH₃,CF₃CH₂OCH₃, CF₃CH₂OCHF₂, CF₃CF₂CH₂OCH₃, CF₃CF₂CH₂OCHF₂,CF₃CF₂CH₂O(CF₂)₂H, CF₃CF₂CH₂O(CF₂)₂F, HCF₂CH₂OCH₃, H(CF₂)₂OCH₂CH₃,H(CF₂)₂OCH₂CF₃, H(CF₂)₂CH₂OCHF₂, H(CF₂)₂CH₂O(CF₂)₂H, H(CF₂)₂CH₂O(CF₂)₃H,H(CF₂)₃CH₂O(CF₂)₂H, (CF₃)₂CHOCH₃, (CF₃)₂CHCF₂OCH₃, CF₃CHFCF₂OCH₃,CF₃CHFCF₂OCH₂CH₃, CF₃CHFCF₂CH₂OCHF₂ and combinations thereof.
 6. Theelectrolyte according to claim 1, wherein a total content of theadditive A and the additive B is 0.001%˜30% by weight of theelectrolyte.
 7. The electrolyte according to claim 1, wherein theadditives further comprise additive C selected from a group consistingof nitrile compounds, cyclic ester compounds containing a sulfur-oxygendouble bond, cyclic carbonate compounds, compounds containing acarbon-nitrogen double bond and combinations thereof; the nitrilecompound is selected from a group consisting of alkanes containing 1˜5nitrile groupings, olefins containing 1˜5 nitrile groupings andcombinations thereof; the cyclic ether compound containing asulfur-oxygen double bond is selected from a group consisting of cyclicsulfates, cyclic sulfites, sultones and combinations thereof; thecompound containing a carbon-nitrogen double bond is selected from agroup consisting of compounds containing

and —N═C═N— and combinations thereof.
 8. The method according to claim7, wherein the nitrile compound is selected from a group consisting ofC_(2˜12) alkanes containing 1˜4 nitrile groupings, C_(2˜12) olefinscontaining 1˜4 nitrile groupings and combinations thereof; the cyclicether compound containing a sulfur-oxygen double bond is selected from agroup consisting of compounds shown as Formula V1, compounds shown asFormula V2, compounds shown as Formula V3 and combinations thereof; thecyclic carbonate compound is selected from compounds shown as Formula V4and combinations thereof;

R₅₁, R₅₂, R₅₃ and R₅₄ are respectively selected from a group consistingof substituted or unsubstituted C_(1˜4) alkylenes and substituted orunsubstituted C_(2˜4) alkenylenes, wherein each substituting group isselected from a group consisting of halogens and C_(2˜4) alkenyls. 9.The electrolyte according to claim 7, wherein the additive C is selectedfrom a group consisting of acetonitrile, propionitrile, butyronitrile,valeronitrile, butenenitrile, 2-methyl-3-butenenitrile, malononitrile,succinonitrile, glutaronitrile, hexanedinitrile, fumarodinitrile,1,2-ethylene sulfate, 1,3-propylene sulfate, 1,3-propylene sulfite,1,3-propane sultone, 1,4-butane sultone, prop-1-ene-1,3-sultone,vinylene carbonate, fluoroethylene carbonate, fluorovinylene carbonate,1,2-difluorovinylene carbonate, vinyl ethylene carbonate,dicyclohexylcarbodiimide and combinations thereof; a content of theadditive C is preferably 0.01%˜10% by weight of the electrolyte.
 10. Alithium-ion battery, comprising a positive electrode plate containing apositive electrode active material, a negative electrode platecontaining a negative electrode active material, a separator for lithiumbattery and the electrolyte according to claim 1.